Fix: Gas Consumption Failure In Acceptance Tests

In the realm of software development, ensuring the reliability and accuracy of tests is paramount. This article delves into a recent issue encountered during acceptance tests, specifically a discrepancy in gas consumption calculations. We will explore the problem, its root cause, the steps taken to reproduce it, and the broader implications for the Hiero network.

Understanding the Issue

In acceptance testing, a critical aspect is verifying the gas consumed by transactions against the gas recorded in the actions sidecar. A mismatch in these values indicates a potential flaw in the system's gas estimation or accounting mechanisms. This issue surfaced during acceptance tests, revealing a discrepancy between the expected gas consumption and the actual gas consumption. The tests, designed to validate the functionality of the Hiero network, flagged an inconsistency in gas calculations, raising concerns about the accuracy of resource management within the system.

Gas consumption is a fundamental concept in blockchain technology, representing the computational effort required to execute a transaction or smart contract. Inaccurate gas calculations can lead to various problems, including transaction failures, unexpected costs, and even security vulnerabilities. Therefore, identifying and resolving gas consumption discrepancies is crucial for maintaining the integrity and efficiency of the Hiero network.

The error message, expected: 561864L but was: 562006L, clearly illustrates the problem. The test expected a gas consumption of 561864 units, but the actual consumption was 562006 units. While the difference may seem small, it highlights a systemic issue in gas calculation, which could have more significant consequences in complex transactions or under heavy network load. This discrepancy prompted a thorough investigation into the underlying cause and the implementation of corrective measures.

The discrepancy was found during the execution of an Ethereum feature test, specifically while creating a contract using a Legacy Ethereum transaction. The test failure occurred in the verifyGasConsumed method, indicating that the gas consumption mismatch was directly related to the contract creation process. This narrowed the focus of the investigation to the gas estimation and accounting mechanisms involved in handling Legacy Ethereum transactions within the Hiero network.

Root Cause Analysis

The root cause of the gas consumption mismatch was traced back to a change introduced in version 0.69 of the consensus node. This change, implemented via this pull request, likely altered the gas calculation logic or the way gas consumption is recorded. Understanding the specifics of this change is crucial to implementing an effective solution.

To effectively address the issue, it's essential to understand the specifics of the change introduced in pull request #22131. This involves examining the code modifications, identifying the sections related to gas calculation, and analyzing how these changes could lead to discrepancies in the reported gas consumption. The investigation may involve comparing the gas calculation logic before and after the change, scrutinizing the data structures used to store gas consumption information, and tracing the flow of gas-related data throughout the transaction processing pipeline.

The change in the consensus node likely impacted the way gas is measured or reported, leading to the observed discrepancy. It's possible that the new gas calculation logic introduced subtle differences in the estimation of gas costs for certain operations, or that the way gas consumption is recorded in the actions sidecar was altered. Whatever the specific mechanism, the change resulted in a mismatch between the expected and actual gas consumption, triggering the test failure.

Steps to Reproduce

To replicate the issue and facilitate debugging, the following steps were outlined:

1. Execute the acceptance tests using the Gradle command: ./gradlew :test:acceptance --info -Dcucumber.filter.tags=@acceptance

This command triggers the execution of acceptance tests, specifically those tagged with @acceptance. The --info flag provides detailed logging output, which can be helpful for diagnosing the issue. By following these steps, developers can reliably reproduce the gas consumption mismatch and gain a deeper understanding of its behavior.

The Gradle command serves as a crucial tool for reproducing the issue. It allows developers to run the acceptance tests in a controlled environment, ensuring that the same conditions that triggered the original failure are replicated. The --info flag is particularly valuable, as it provides detailed logging information that can help pinpoint the exact location of the error and the sequence of events leading up to it. This detailed logging is essential for effective debugging and troubleshooting.

The use of the cucumber.filter.tags=@acceptance option further streamlines the reproduction process. By filtering the tests to include only those tagged with @acceptance, developers can focus on the specific tests that are relevant to the gas consumption issue. This reduces the amount of noise in the test results and makes it easier to identify the root cause of the problem. The ability to selectively run tests is a powerful feature of testing frameworks, enabling developers to efficiently target specific areas of the system for validation.

Contextual Information

Additional context was provided to aid in the investigation:

• Logs from the mirror node REST API interactions, showing successful retrieval of contract and transaction data.
• The specific scenario that failed: creating a contract using a Legacy Ethereum transaction.
• The expected and actual gas consumption values.
• The Hedera network in use: previewnet.
• The version of the software: v0.144.0-rc1.
• The operating system: None (indicating a platform-independent issue).

The provided logs offer a valuable snapshot of the system's behavior during the test execution. They show the interactions with the mirror node REST API, including the successful retrieval of contract details, transaction results, and block information. These logs confirm that the mirror node was functioning correctly and that the necessary data was available. However, the logs also highlight the discrepancy in gas consumption, providing concrete evidence of the issue.

The fact that the failure occurred during a Legacy Ethereum transaction is significant. Legacy transactions use a different gas calculation mechanism compared to newer transaction types, such as EIP-1559 transactions. This suggests that the gas consumption mismatch may be specific to Legacy transactions or that the changes in the consensus node had a disproportionate impact on this type of transaction. This observation narrows the scope of the investigation and helps focus efforts on the gas calculation logic associated with Legacy transactions.

The information about the Hedera network (previewnet) and the software version (v0.144.0-rc1) is also crucial. It allows developers to reproduce the issue in the same environment and to track down the specific changes that were introduced in that version. The fact that the operating system is listed as